Wastewater recycling

WHILE it may seem polite to keep the lid on toilet talk, if you’re pursuing household sustainability, you can’t ignore your sewer.

Rita Narangala, engineer at Yarra Valley Water, explains that our sewerage system not only consumes buckets of potable water, but also demands electricity for pumping and treating.

“It’s something a lot of people don’t immediately think about, but sewage is actually quite energy intensive to collect and treat,” she says. “When you install efficient fittings, it’s a real double-whammy in terms of the savings in water and in the energy for supplying the water and treating the sewage.”

In Kinglake West, Yarra Valley Water is building a research project that changes the way the company deals with our pipes. It undertook a life cycle assessment of wastewater options for the environmentally sensitive area, which is bordered by national park.

When the plumbing and infrastructure is complete, up to 90 homes will have an alternative sewerage service, comprising urine diverting toilets, greywater treatment and reuse systems, and a pressure sewer.

The measures are expected to halve wastewater discharge, slash nutrient discharge by about 80 per cent, and cut greenhouse gas emissions by one-third compared with a conventional sewer.

One element of the approach in Kinglake West is a switch from “nutrient removal” to “nutrient recovery”; that is, turning the problem into a solution.

Presently, the high-nutrient content in effluent can cause pollution in our waterways and bays. It’s a problem that must be overcome by extensive and expensive treatment. At the same time, however, our farmers buy in artificial fertilisers in a quest to boost their soil fertility.

“Urine is rich in phosphorus and nitrogen, so diverting it is an easy way to capture a small fraction of the wastewater, which is nutrient-rich and relatively low in bacteria and pathogens as well,” Ms Narangala says.

Yarra Valley Water will work with a local farmer to trial the use of urine as a fertiliser replacement (most likely on a non-food crop, such as turf). Projects of this kind are well advanced overseas, especially in Scandinavia.

“Phosphorus is an essential plant nutrient – there’s really no replacement for it,” Ms Narangala says. “But there’s a view amongst scientists that reserves could run out in the next few generations. The peak level of production, after which demand outstrips supply, could occur much sooner.

“We need to find alternative nutrient sources – human waste is one, as well as efficiency gains in the way it’s mined and the way we produce food.”

While the solutions adopted by Yarra Valley Water in its Kinglake West project are specifically designed to suit local conditions, they’re a sign of changes in the pipeline elsewhere.

In sewered suburbs it’s more difficult to retrofit large-scale greywater and nutrient recycling all at once. But as urban infill and infrastructure upgrades continue, the utilities will seek out solutions that cut water and energy use, and turn nutrient pollution into a resource.

Ms Narangala says decentralised treatment and recycling may become more common. “Our infrastructure is in the ground already, but we’re looking at alternatives to simply replacing parts when necessary. Water companies recognise that we’re in a unique position to recover and reuse nutrients. The industry is assessing the best ways to build a sustainable sewage system.”